By Scott Stewart
The next 4 to 5 weeks is the time to consider making a foliar application for aphids in wheat. I've discussed the potential value of managing aphids to prevent the spread of barley yellow dwarf virus, or BYDV. A late-winter, foliar insecticide application, at least on wheat not having an insecticide seed treatment, has shown a consistent yield benefit in my testing over the last five years.
Over the last several years, we've studied how seed treatment or foliar insecticides impact wheat yields. Presumably, most of the effects we have seen are the result of aphid control and a reduction in BYDV. We routinely see both in our tests.
Insecticide seed treatments increased yield on average about 3-4 bushels per acre. This is consistent with previous data generated in Tennessee. It is uncommon to find many aphids in wheat planted in mid-October. This observation typically holds true until late February or March when the wheat and aphid populations begin to grow.
A late winter, or around February, foliar application of insecticide has increased yields in my tests by an average of 8.4 bushels per acre. This is for wheat not having an insecticide seed treatment.
My experience, based on less data, is that using both an insecticide seed treatment and a late winter foliar insecticide application is not necessary IF you plant in mid-October or later. In other words, the benefits of the seed treatment and the foliar application are probably not additive.
A seed treatment or foliar application of insecticide in the fall and spring may be necessary for wheat that is planted too early … or if aphid populations get an unusually early start. Scouting can help determine if a fall application of insecticide is needed for the prevention of BYDV.
I do not think the timing of this application is especially critical, BUT it must be made before aphids have become well established in the field. Otherwise, you've missed the opportunity to prevent the transmission of BYDV. You are likely too late if aphid populations already exceed 6-8 aphids per foot of row.
Stewart is an entomologist with the University of Tennessee Extension.